This application is based on Application No. 2001-182989, filed in Japan on Jun. 18, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a control system for an internal combustion engine, and in particular to ignition timing control of such a control system.
2. Description of the Related Art
FIG. 12 is a view schematically illustrating the construction of this kind of known control system for an internal combustion engine. In this figure, the known control system includes an internal combustion engine control unit (ECU) 1, a reference signal generator 3 for generating a reference signal representative of a reference position of the rotational position of an engine, and an ignition (IG) coil 8 connected with a spark plug 9. The ECU 1 includes a CPU 2 acting as an arithmetic processing section, a reference signal input I/F circuit 5, an IG coil drive output I/F circuit 7 connected with the ignition (IG) coil 8, and a RAM 11 acting as a temporary storage device. The CPU 2 includes a timer TM1 which is constituted by software. Here, note that the output side of the CPU 2 in FIG. 12 illustrates the configuration for one cylinder.
FIG. 13 is a time chart of signals at respective portions of the system of FIG. 12.
In the past, the ECU 1 has an ignition timing control function as one of its various control functions. For a control method of an ignition system, there is known a full transistor method in which energization start timing and energization cut-off timing to an IG coil are controlled to accumulate energy therein, and these timing are generally controlled by a CPU. In addition, these timing are important items for engine power and the stability thereof, and hence accurate control and high control accuracy are required.
As such a concrete full transistor control method, there is used a predetermined single timer to which the timing for starting energization is set with a predetermined timing signal (i.e., signal representative of a reference angle position of the rotational position of the engine) taken as a reference. Then, after start of energization, the timing of cutting off an energizing current is set to this timer. Ignition timing is the timing at which a high voltage is developed in an IG coil thereby to generate a spark in a spark plug connected therewith, and hence the timing of cutting off the energizing current is the ignition timing. That is, two timing (i.e., the timing of energization and the timing of cutting off the energization) is controlled by the single timer.
Now, the concrete content of such control will be described below. In the known system configuration of FIG. 12, connected with the ECU 1 are the reference signal generator 3, the IG coil 8 and the spark plug 9 for supplying an optimum amount of ignition energy to an internal combustion engine (hereinafter sometimes simply referred to as an engine) at optimal timing.
The reference signal input I/F circuit 5 of the ECU 1 serves to detect a signal from the reference signal generator 3, and upon detection of a reference signal, the reference signal input I/F circuit 5 converts it into a signal which can be controlled by the CPU 2, and supplies it to the CPU 2 as reference timing. The CPU 2 calculates optimal energization timing and optimal cut-off timing to the IG coil 8 based on the reference timing, and supplies a control output to the IG coil drive output I/F circuit 7, thereby driving the IG coil 8.
FIG. 13 illustrates signal waveforms at respective portions of FIG. 12. A signal from the reference signal generator 3 is passed through the reference signal input I/F circuit 5, so that the waveform of the signal S1 input to the CPU 2 is converted into a reference signal of a rectangular waveform of a high (H) level representative of reference timing for control of ignition timing such as, for example, BTDC 70xc2x0 (i.e., a position of a crank angle of 70xc2x0 before top dead center). The CPU 2 calculates the rotational speed of the engine from the reference timing, and optimal ignition timing and optimal energization time based on information from various sensors. Based on the results of these calculations, the CPU 2 controls energization start timing T1 and ignition (energization cut-off) timing T2 to the IG coil 8, for example, by using the timer TM1 of a predetermined time resolution, which is operated by clock pulses of a predetermined time resolution in the CPU 2.
Specifically, at a time point of the reference signal (BTDC 70xc2x0), the energization start timing T1 is set to the timer TM1, and the timer TM1 is driven to start operation. At the same time, the ignition (cut-of timing T2 is stored at a predetermined position of the RAM 11. When the timer TM1 performs counting and reaches the energization start timing T1 previously set, an interrupt is generated so that the output signal S2 from the CPU 2 to the IG coil drive output I/F circuit 7 is changed from the L level to the H level, whereby the IG coil 8 starts to be energized, as illustrated at a waveform S3 in FIG. 13, thus accumulating energy therein.
Subsequently, the ignition (cut-off) timing T2 previously stored in the RAM 11 is set to the timer TM1, and the timer TM1 is driven to start counting. When the timer TM1 reaches the ignition (cut-oft) timing T2 thus set, an interrupt is generated so that the output signal S2 from the CPU 2 to the IG coil drive output I/F circuit 7 is changed from the H level to the L level, thereby causing the IG coil 8 to generate an ignition output from its secondary side to the spark plug 9 as illustrated at waveforms S3 and S4 in FIG. 13. Thereafter, each time the reference timing (reference signal S1) is generated and input to the CPU 2, the CPU 2 performs control and output in the same way as described above, whereby the engine is controlled in a stable manner.
In general, in a four-cycle engine having four cylinders, the ECU controls four or two ignition coils, and in a four-cycle engine having six cylinders, the ECU controls six or three ignition coils. In contrast to this, in two-cycle engines, it is necessary to control IG coils corresponding in number to cylinders according to the configuration and control processes of the engine, and hence in a two-cycle engine having four cylinders, four ignition coils must be controlled, and in a two-cycle engine having six cylinders, six ignition coils must be controlled. That is, in the case of two-cycle engines, the CPU is required to have timers corresponding in number to engine cylinders (i.e., the number of IG coils) in order to perform ignition timing control.
FIG. 14 illustrates a concrete example of the configuration of a known control system for an internal combustion engine; FIG. 15 illustrates a time chart of signals at respective portions of the system of FIG. 14; and FIGS. 16 through 18 illustrate the operation of the system of FIG. 14. In these figures, the same or corresponding parts as those of FIGS. 12 and 13 are identified by the same symbols.
Now, the operation of this known control system will be described below with reference to these figures. As described above, in the case of two-cycle engines, IG coils 8 corresponding in number to the cylinders must be controlled and driven independently of one another, and hence in a two-cycle engine having n cylinders for instance, the reference signal generator 3 generates n reference signals so that reference timing (reference signal S1) is input to the CPU 2 via the reference signal input I/F circuit 5. When the reference timing is input to the CPU 2, a reference signal interrupt is generated (step S100 of FIG. 16), and a check is made as to which cylinder generates the current interrupt (step S101), and then respective cylinders are processed as described below (step S103).
In the case where the cylinder having generated the current interrupt is cylinder #1 for example (step S103 of FIG. 17), energization start timing (T1-1) is set to the timer TM1 for cylinder #1, and the timer TM1 is driven to start counting (step S1031), and ignition (cut-off) timing (T2-1) is set to a predetermined position in the RAM 11 (step S1033). Thereafter, the remaining processing is carried out (step S1035), and then the current interrupt processing is ended.
Subsequently, when the timer TM1 reaches the energization start timing (T1-1) as previously set, an interrupt is generated by the timer TM1 (step S105 of FIG. 18). A check is made as to whether the content of the current interrupt is energization start processing or ignition (cut-off) processing (step S1051).
In the case of energization start timing (step S1053), the output of the CPU 2 to an IG coil drive output I/F circuit 7 which controls and drives an IG coil 8 for cylinder #1 is switched from the L level to the H level, thereby starting energization of the corresponding IG coil 8 for cylinder #1 (step S10531). Thereafter, the ignition (cut-off timing (T2-1) stored in the predetermined position in the RAM 11 is set to the timer TM1, and the timer TM1 is driven to start counting (step S10533), thus completing the interrupt processing.
On the other hand, in the case of ignition (cut-off timing (step S1055), the output of the CPU 2 to an IG coil drive output I/F circuit 7 which controls and drives an IG coil 8 for cylinder #1 is switched from the H level to the L level, thereby generating an ignition output to the corresponding IG coil 8 for cylinder #1 (step S10551). Here, note that in the case of cylinder #2, similar setting and driving processing is carried out for the timer TM2 for cylinder #2.
In the known control system for an internal combustion engine as constructed above, as the number of timers to be used for control increases, a CPU of higher performance is required, resulting in an expensive one of high performance specifications. Thus, the cost of the CPU increases, and hence the cost of the internal combustion engine control unit (ECU) as a whole rises, too. In addition, the CPU of high performance generally has an increased size, so there is a tendency that the size of internal combustion engine control unit (ECU) also increases. At present, the small size, lightness and low cost are demanded of an internal combustion engine control unit (ECU), and there arises a problem that the above tendency makes it difficult to satisfy these demands.
The present invention is intended to obviate the problem as referred to above, and has for its object to provide a control system for an internal combustion engine which is capable of satisfying the demand of reducing the size, weight and cost of an internal combustion engine control unit (ECU), and at the same time fulfilling sufficient timing accuracy for ignition timing.
Bearing the above object in mind, the present invention resides in a control system for an internal combustion engine, including: a reference signal generator having a plurality of terminals and generating from the terminals reference signals representative of reference positions of the rotational position of the engine for respective cylinders; a fixed angle generator for generating a fixed angle signal which has a resolution higher than that of the reference signals and which represents the rotational position of the engine; and an internal combustion engine control unit with an arithmetic processing unit which receives the reference signals and the fixed angle signal to carry out ignition timing control. The internal combustion engine control unit determines a predetermined cylinder from the reference signals, controls energization start timing and energization cut-off timing to an IG coil for the predetermined cylinder based on count values of the fixed angle signal with a corresponding one of the reference signals taken as a reference, performs energization start control and energization cut-off control when the count values are counted up, respectively, and thereafter performs energization start control and energization cut-off control to IG coils for the remaining cylinders, respectively, in a sequential manner at timing at which the fixed angle signal is counted up to a count value corresponding to an intercylinder interval between the cylinders until the next control of the predetermined cylinder comes.
In a preferred form of the present invention, the internal combustion engine control unit includes a storage section for storing a table including crank angles representative of engine rotational angles from each of the reference signals to an ideal energization start timing and an ideal energization cut-off timing to each IG coil in respective operating conditions. The arithmetic processing section includes counters for controlling energization start timing and energization cut-off timing, respectively, to the IG coils, to which counters count values of the fixed angle signal corresponding to crank angles are set respectively according to the table, so that the counters count up to the set values, respectively, at the time of controlling the predetermined cylinder, and thereafter the count value corresponding to the intercylinder interval between the cylinders are set to the counters, which then count the fixed angle signal up to the set count value.
In another preferred form of the present invention, the arithmetic processing section of the internal combustion engine control unit sets the count values to the counters, also sets a cylinder to be controlled to the storage section, and refers to the cylinder to be controlled which is stored in the storage section during control.
In a further preferred form of the present invention, the reference signal generator generates the reference signals from separate terminals provided one for each cylinder. The internal combustion engine control unit has input terminals provided one for each cylinder for receiving the reference signals. The arithmetic processing section identifies the cylinders based on from which input terminals the reference signals are input to the internal combustion engine control unit.
In a still further preferred form of the present invention, the arithmetic processing section of the internal combustion engine control unit determines the operating conditions from a cycle of the reference signals input thereto.
Particularly, a control system for an internal combustion engine according to the present invention includes a reference signal generator for generating reference signals representative of reference positions of the rotation position of the engine, a fixed angle signal generator for generating a fixed angle signal, and an internal combustion engine control unit (ECU) for detecting and receiving these signals and generating a drive output to each IG coil. The ECU includes a CPU, and the CPU constitutes two counters for counting the fixed angle signal based on the reference signals. One of the counters serves to control energization start timing to the IG coils, and the other counter serves to control ignition (cut-off) timing to the IG coils.
By employing an angle counting method in which the fixed angle signal is counted by means of the two counters based on the reference signals to control the energization start timing and the ignition (energization cut-off) timing to the IG coils, the use of only two counters constituted by the CPU is sufficient for controlling the IG coils even where the number of IG coils is more than two, thus making it possible to construct the system by using an inexpensive UPU. Consequently, the internal combustion engine control unit (ECU) can be reduced in size, weight and cost. Moreover, it is possible to achieve a system which can satisfy sufficient timing accuracy in the ignition timing. In addition, due to the use of the angle counting method, it is possible to perform particularly accurate ignition timing control even during idling, acceleration, deceleration, etc., in which variations in rotation of the engine are great.
The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of a preferred embodiment of the present invention taken in conjunction with the accompanying drawings.